Oxidation of benzyl alcohols to ketones and aldehydes by O3 process enhanced using high-gravity technology

In this study, a practical process for ozonization of benzyl alcohols to ketones and aldehydes in a rotating packed bed(RPB-O_3) reactor has been developed. Using 1-phenylethanol as a model reactant, the performance of RPB-O_3 process in different solvents has been compared with the commonly used stirred tank reactor(STR-O_3). Ethyl acetate was the optimum solvent for the conversion of 1-phenylenthanol to acetophenone in RPB-O_3 process, with 78% yield after 30 min. In a parallel STR-O_3 experiment, the yield of acetophenone was50%. Other experimental variables, i.e. O_3 concentration, reaction time, high-gravity factor and liquid flow rate were also optimized. The highest yield of acetophenone was obtained using O_3 concentration of 80 mg·L~(-1),reaction time of 30 min, high gravity factor of 40 and liquid flow rate of 120 L·h~(-1). Under the optimized reaction conditions, a series of structurally diverse primary and secondary alcohols was oxidized with(19%–92%) yield.The ozonization mechanism was studied by Electron Paramagnetic Resonance(EPR) spectroscopy, monitoring the radical species formed upon self-decomposition of O_3. The characteristic quadruple peak with the 1:2:2:1 intensity ratio that corresponds to hydroxyl radicals(·OH) was observed in the electron paramagnetic resonance(EPR) spectrum, indicating an indirect oxidation mechanism of alcohols via ·OH radical.     

Monodispersed gold nanoparticles supported on γ-Al2O3 for enhancement of low-temperature catalytic oxidation of CO

Monodispersed nano-Au/γ-Al₂O₃ catalysts for low-temperature oxidation of CO have been prepared via a modified colloidal deposition route, which involves the deposition of dodecanethiolate self-assembled monolayer (SAM)-protected gold nanoparticles (C₁₂ nano-Au) in hexane on γ-Al₂O₃ at room temperature. The diameter of the gold nanoparticles deposited on the support is 2.5 ± 0.8 nm after thermal treatment, and their valence states comprise both the metallic and oxidized states. It is found that the thermal treatment temperature affects significantly the catalytic activity of the catalysts in the processing steps. The catalyst treated at 190 °C exhibits considerably higher activity as compared to catalysts treated at 165 and 250 °C. A 2.0-wt.% nano-Au/γ-Al₂O₃ catalyst treated at 190 °C for 15 h maintains the catalytic activity at nearly 100% CO oxidation for at least 800 h at 15 °C, at least 600 h at 0 °C, and even longer than 450 h at −5 °C. Evidently, the catalysts obtained using this preparation route show high catalytic activity, particularly at low temperatures, and a good long-term stability.     

SiO2负载MoP催化剂的制备及其对苯甲醇选择性氧化的催化性能

在SiO2载体上，以乙酰丙酮钼与次磷酸铵为原料，未经煅烧直接还原制备负载型磷化钼（MoP/SiO2）催化剂，通过XRD、N2-物理吸附、TEM和XPS等手段对催化剂进行表征。研究了浸渍液中P/Mo摩尔比（n(P):n(Mo)=1:1，2:1，3:1）、还原温度（500、550、600 ℃）对MoP相的影响，并考察其在苯甲醇选择性氧化生成苯甲醛反应中的催化性能。结果表明，浸渍液中P/Mo摩尔比为2、还原温度为550 ℃时，所获得的MoP/SiO2催化剂（MoP/SiO2-550-2）在苯甲醇选择性氧化生成苯甲醛反应中具有最好的转化率（99.7%）和优异的产物选择性（99.8%），这是由于MoP/SiO2-550-2催化剂上形成了更多小颗粒的MoP相。     

Liquid phase selective oxidation of benzyl alcohol over Pd–Ag catalysts supported on pumice

Selective oxidation of benzyl alcohol to benzaldehyde was carried out over pumice supported bimetallic and monometallic Pd and Ag catalysts. Preliminary kinetic studies were performed at 333 K in autoclave, at pressure of 2 atm in pure oxygen. Under these conditions, small amounts of benzoic acid were detected with the monometallic Pd pumice being the most active catalyst. The reaction was also carried out under flowing oxygen at atmospheric pressure and at 348 K. Under these conditions, the selectivity to benzaldehyde was 100%. The catalytic activity of the catalysts was measured after different oxidation and reduction treatments at high temperature. In addition, two mechanical mixtures of pretreated Pd and Ag monometallic samples were tested. The structural data (XRD, XPS, EXAFS) along with the catalytic results would indicate that Ag⁰ and Pd⁰ species are the catalytic sites acting with certain synergism.     

K/Ni/β-Mo2C: A highly active and selective catalyst for higher alcohols synthesis from CO hydrogenation

Nickel and potassium promoted β-Mo₂C catalysts were prepared for CO hydrogenation to higher alcohols synthesis. The results revealed that β-Mo₂C produced mainly hydrocarbons, but the addition of potassium resulted in a remarkable selectivity shift from hydrocarbons to alcohols over β-Mo₂C. Moreover, it was found that potassium enhanced the ability of chain propagation of β-Mo₂C catalyst and led to a higher selectivity to C₂⁺OH. The addition of nickel further enhanced higher alcohols synthesis, which showed the optimum at 1/8–1/6 of Ni/Mo molar ratios. The characterization suggested that there might be a synergistic effect of potassium and nickel on β-Mo₂C, which favored the alcohols synthesis. The production of alcohols appeared to be relevant to the presence of Mo⁴⁺ species, whereas the formation of hydrocarbons was closely associated with Mo²⁺ and/or Mo⁰ species on the surface of β-Mo₂C-based catalysts.     

Adsorption properties of a Pd/γ-Al2O3 catalyst using inverse gas chromatography

The adsorption properties of a commercial Pd/Al₂O₃ catalyst were studied and compared with those of the Al₂O₃ support of the same specific surface area. Inverse gas chromatography (IGC) was used to determine the adsorption isotherms of five n-alkanes (C₈–C₁₂) in the 200–230 °C temperature range. Moreover, heats of adsorption, solubility coefficients and free energy of adsorption, are also reported. Interaction parameters of polar molecules with the stationary phase have also been determined and compared with those for the n-alkanes. Experiments with both the reduced and oxidized catalyst have been carried out by IGC and the results compared with those obtained by temperature programmed reduction (TPR) experiments.     

The role of H2O in the photocatalytic oxidation of toluene in vapour phase on anatase TiO2 catalyst: A FTIR study

Photocatalytic oxidation of toluene has been carried out in a gas–solid regime by using polycrystalline anatase TiO₂ in a fixed-bed continuous reactor. Air containing toluene and water vapours in various molar ratios was fed to the photoreactor irradiated by a medium pressure Hg lamp. Toluene was mainly photo-oxidised to benzaldehyde, and small amount of benzene, benzyl alcohol and traces of benzoic acid and phenol were also detected. In the presence of water, no decrease of photoreactivity was observed at steady-state conditions. By removing water vapour from the feed, the conversion of toluene to benzaldehyde was almost completely inhibited, and an irreversible deactivation of the catalyst occurred. FTIR investigations indicated that benzaldehyde is photoproduced on the TiO₂ surface even in the absence of water vapour, but exposure of the catalyst to the UV light in a dry atmosphere results in an irreversible consumption of surface hydroxyl groups. As these species play a key role in the photoreactive process, this dehydroxylation should be the reason of the catalyst deactivation observed in the catalytic runs carried out in the absence of water vapour.     

Fischer–Tropsch synthesis with Co/SiO2–Al2O3 catalyst and steady-state modeling using artificial neural networks

This paper reports the results of an experimental study involving Fischer–Tropsch synthesis on Co/SiO₂–Al₂O₃ catalyst. The objective of the study was to find the reaction conditions for achieving an optimal selectivity with respect to -liquid hydrocarbons. The experimental data on reaction conversion and steady-state concentrations of different product species has been used to develop artificial neural-network-based models which are generic and can be used for predicting the reaction behaviour under different operating conditions.     

Electrochemical promotion of a platinum catalyst supported on the high-temperature proton conductor La0.99Sr0.01NbO4−δ

The recently discovered, high-temperature proton conductor, La_0.99Sr_0.01NbO_4−δ, was used as a support for the electrochemical promotion of a platinum catalyst. Ethylene oxidation was used as a probe reaction in the temperature range 350–450 °C. Moderate non-Faradaic rate modification, attributable to a protonic promoting species, occurred under negative polarisation; some permanent promotion was also observed. In oxidative atmospheres, both the p_O2 of the reaction mixture and the temperature influenced the type and magnitude of the observed rate modification. Rate-enhancement values of up to ρ = 1.4 and Faradaic-efficiency values approaching Λ = −100 were obtained. Promotion was observed under positive polarisation and relatively dry, oxygen-rich atmospheres suggesting that some oxygen ion conductivity may occur under these conditions. Impedance spectroscopy performed in atmospheres of 4 kPa O₂/N₂ and of 5 kPa H₂/N₂ under dry and slightly humidified (0.3 kPa H₂O) conditions indicated that the electrical resistivity is heavily dominated by the grain-boundary response in the temperature range of the EPOC studies; much lower grain-boundary impedances in the wetter conditions are likely to be attributable to proton transport.     

Preparation of H5PMo10V2O40 catalyst immobilized on nitrogen-containing mesostructured cellular foam carbon (N-MCF-C) and its application to the vapor-phase oxidation of benzyl alcohol

Nitrogen-containing mesostructured cellular foam carbon (N-MCF-C) was synthesized by a templating method using mesostructured cellular foam silica (MCF-S) and polypyrrole as a templating agent and a carbon precursor, respectively. The N-MCF-C was then modified to have a positive charge, and thus, to provide a site for the immobilization of [PMo₁₀V₂O₄₀]⁵⁻. By taking advantage of the overall negative charge of [PMo₁₀V₂O₄₀]⁵⁻, H₅PMo₁₀V₂O₄₀ (PMo₁₀V₂) catalyst was chemically immobilized on the N-MCF-C support as a charge-matching component. Characterization results showed that the PMo₁₀V₂ catalyst was finely dispersed on the N-MCF-C support via strong chemical interaction, and that the pore structure of N-MCF-C was still maintained even after the immobilization of PMo₁₀V₂. In the vapor-phase oxidation of benzyl alcohol, the PMo₁₀V₂/N-MCF-C catalyst showed a higher conversion and a higher oxidation activity (formation of benzaldehyde) than the unsupported PMo₁₀V₂ and PMo₁₀V₂/MCF-S catalysts.     

CO oxidation and CO2 reduction on carbon supported PtWO3 catalyst

The activity of a carbon supported PtWO₃ (PtWO₃/C) catalyst in the CO oxidation and CO₂ reduction reactions was evaluated in sulfuric acid solution at room temperature.Cyclic voltammetry combined with on-line mass spectrometry shows that the oxidation of both saturated CO adlayer and dissolved CO on PtWO₃/C material commences at rather low potentials, ca. 0.18 and 0.12 V vs. RHE, respectively. However, the low-potential process seems to involve only a minor fraction of the CO adlayer, the major part of the adsorbed CO layer being oxidised at the potentials as high as those for pure Pt catalysts—ca. 0.7 V vs. RHE. PtWO₃/C material was found to reversibly de-activate upon a prolonged exposure to the CO-saturated solution due to the inhibition of the hydrogen tungsten bronze formation.The reduction of CO₂ on PtWO₃/C leads to the formation of an adsorbate - presumably CO - on the Pt sites of the catalyst. Although the rate of the adsorbate build-up on PtWO₃/C at 0.1 V is lower than that on pure Pt/C, our results indicate that upon a prolonged exposure of the PtWO₃/C electrode to a CO₂-saturated solution a complete poisoning of the Pt sites with the adsorbate is likely to occur at room temperature.     

Synthesis of mixed alcohols from CO2 contained syngas on supported molybdenum sulfide catalysts

The performances of active carbon supported molybdenum sulfide catalysts prepared by different procedures or promoted by different elements in the synthesis of mixed alcohols from CO₂ containing syngas were examined. The results showed that high alcohol activity and selectivity could be obtained by employing a rapid drying procedure and employing a H₂S---H₂ stream for (NH₄)₂MoS₄ decomposition. Addition of Co, Cr and Cl to K---Mo/C catalyst led to an increase in the alcohol activity or selectivity. The presence of CO₂ in the feed caused a greater amount of water to be produced but reduced the formation of CO₂. The product distribution was also strongly influenced by the presence of either CO₂ or H₂S in the feed. Addition of CO₂ reduces the formation of higher alcohols while H₂S increases higher alcohol formation.     

盐酸二甲胺三氧化铬／硅胶的制备及其应用

研究了盐酸二甲胺三氧化铬／硅胶的制备方法及其对醇类的氧化性能。该试剂制备简单,制备与氧化过程中均不产生含铬废液,并且性能稳定、易保存。对醇的氧化反应收率高、条件温和、操作简单。为铬（Ⅵ）氧化剂用于清洁生产提供了依据。     

Conversion of biomass to fuel: Transesterification of vegetable oil to biodiesel using KF loaded nano-γ-Al2O3 as catalyst

KF-impregnated nanoparticles of γ-Al₂O₃ were calcinated and used as heterogeneous catalysts for the transesterification of vegetable oil with methanol for the synthesis of biodiesel (fatty acid methyl esters, FAME). The ratio of KF to nano-γ-Al₂O₃, calcination temperature, molar ratio of methanol/oil, transesterification reaction temperature and time, and the concentration of the catalyst were used as the parameters of the study. A methyl ester yield of 97.7 ± 2.14% was obtained under the catalyst preparation and transesterification conditions of KF loading of 15 wt%, calcination temperature of 773 K, 8 h of reaction time at 338 K, and using 3 wt% catalysts and molar ratio of methanol/oil of 15:1. This relatively high conversion of vegetable oil to biodiesel is considered to be associated with the achieved relatively high basicity of the catalyst surface (1.68 mmol/g) and the high surface to volume ratio of the nanoparticles of γ-Al₂O₃.     

Improvement of thermal stability of NO oxidation Pt/Al2O3 catalyst by addition of Pd

The present work has been undertaken to tailor Pt/Al₂O₃ catalysts active for NO oxidation even after severe heat treatments in air. For this purpose, the addition of Pd has been attempted, which is less active for this reaction but can effectively suppress thermal sintering of the active metal Pt. Various Pd-modified Pt/Al₂O₃ catalysts were prepared, subjected to heat treatments in air at 800 and 830 °C, and then applied for NO oxidation at 300 °C. The total NO oxidation activity was shown to be significantly enhanced by the addition of Pd, depending on the amount of Pd added. The Pd-modified catalysts are active even after the severe heat treatment at 830 °C for a long time of 60 h. The optimized Pd-modified Pt/Al₂O₃ catalyst can show a maximum activity limited by chemical equilibrium under the conditions used. The bulk structures of supported noble metal particles were examined by XRD and their surface properties by CO chemisorption and EDX-TEM. From these characterization results as well as the reaction ones, the size of individual metal particles, the chemical composition of their surfaces, and the overall TOF value were determined for discussing possible reasons for the improvement of the thermal stability and the enhanced catalytic activity of Pt/Al₂O₃ catalysts by the Pd addition. The Pd-modified Pt/Al₂O₃ catalysts should be a promising one for NO oxidation of practical interest.     

Study of induction period over K2CO3/MoS2 catalyst for higher alcohols synthesis

The K₂CO₃/MoS₂ catalyst for higher alcohols synthesis with synthesis gas as feedstock was prepared. The catalyst was characterized by TPR, in-situ XPS, XRD and SEM. Effects of pretreatment with H₂, CO or synthesis gas on activity and selectivity of the catalyst were investigated. Results showed that there was a remarkable induction period about 180 h at the initial reaction stage for the un-treated catalyst. The catalytic performances for alcohols synthesis changed notably during the induction period. The induction period was confirmed to be resulted primarily from the sulfur losing and K element dispersion on the surface of ADM catalysts. Pretreatment of the catalyst could remarkably shorten the time of induction period as well as promote the catalytic activity. Furthermore, the higher alcohols (C₂ + OH) content in the liquid products were enhanced after the catalyst pretreated by CO or synthesis gas which could be ascribed to the increasing of Mo⁴⁺ content on the surface of the catalyst.     

Fabrication of Fe-, Ni- and FeNi-coated Al2O3 core-shell microspheres by heterogeneous precipitation

The precursors with NiCO₃·2Ni(OH)₂·2H₂O-, Fe₂O₃·nH₂O-, or both of NiCO₃·2Ni(OH)₂·2H₂O- and Fe₂O₃·nH₂O-coated alumina microspheres were prepared, respectively, by the aqueous heterogeneous precipitation using metal salts, ammonium hydro-carbonate and -Al₂O₃ micropowders as the starting materials. Subsequently, magnetic metallic Ni-, -Fe- and γ-FeNi-coated alumina core-shell structural microspheres were successfully obtained by thermal reduction of the as-prepared precursors at 700 °C for 2 h, respectively. Optimized precipitation processing parameters of the concentration of alumina micropowders (15 g/L), the rate of adding reactants (5 mL/min) and pH value were determined by a trial and error method. Powders of the precursors and the resultant metal (Ni, -Fe, γ-FeNi alloy)-coated alumina micropowders were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The experimental results show that it is possible to adjust metal coating thicknesses and fabricate multilayer structured metal/ceramics core-shell microspherical powder materials and these materials may be applied for high performance of functional materials and devices.     

Origins of the Rio Capim kaolinites (northern Brazil) revealed by δO and δD analyses

Deuterium (δD) and oxygen (δ¹⁸O) isotope data from the Rio Capim kaolin, northern Brazil, were combined with optical studies in order to better understand the genesis and evolution of the kaolinites. The results show that δ¹⁸O values from a lower soft kaolin unit range from 6.0‰ to 19.2‰ for Ka (size ranging from 1 to 3 μm) and Kb (size ranging from 10 to 30 μm) kaolinites, and from 15.4‰ to 24.9‰ for Kc (size < 200 nm) kaolinites. The δD values range from − 63.1‰ to 79.5‰ for the Ka + Kb kaolinites, and from − 68.8‰ to − 244.35‰ for the Kc kaolinites. An upper semi flint kaolin unit, dominated by Kc kaolinites, displays δ¹⁸O and δD values ranging from 15.1‰ to 21.8‰, and − 71.3‰ to − 87.4‰, respectively. Based on these data, and on the δ¹⁸O and δD values obtained for the surface meteoric water and groundwater, it can be concluded that the kaolinites are not in equilibrium with the modern weathering environment, but they reflect isotopic compositions of the formation time, probably due to the interaction with fossil groundwater. However, mineralogical contaminations derived from replacements of framework grains also had great influence in the isotopic composition of these kaolinites. In addition, the isotope values of the Kc kaolinites from the semi-flint kaolin unit is variable, which is due to the presence of Kc kaolinites of different origins, including kaolinites derived from the underlying soft kaolin unit, kaolinites formed during different phases of paleoweathering, as well as later phases of coarse-grained kaolinites formed along fractures. Due to these complexities, binary diagrams contrasting δ¹⁸O and δD values, worldwide applied for distinguishing supergenic from hypogenic kaolinites, as well as those formed under weathering conditions, can not be applied to interpret the origin of the kaolinites in the Rio Capim Kaolin.     

Friedel–Crafts benzylation of aromatics with benzyl alcohols catalyzed by heteropoly acids supported on mesoporous silica

Heteropoly acids (HPA), such as tungstophosphoric acid (H₃PW₁₂O₄₀ · xH₂O) (HPW), molybdophosphoric acid (H₃PMo₁₂O₄₀ · xH₂O) (HPMo) and tungstosilicic acid (H₄SiW₁₂O₄₀ · xH₂O) (HSiW) were supported on mesoporous silica such as MCM‐41, FSM‐16 and SBA‐15 by the impregnation method to enhance the catalytic activity of these solid acids by their dispersion on the support with high surface area. These supported solid catalysts were used in the benzylation of benzene and substituted aromatics with benzyl alcohol (BnOH). The immobilization enhanced the catalytic performances and HPW supported on MCM‐41 exhibited the best activity for benzylation among the heteropoly acids, although dibenzyl ether (DBE) formation by the dehydration of BnOH also occurred. The mesoporous architecture of the silica enhances the activity of benzylation because of the high dispersion of HPW on the support with high surface area; however, no steric restriction by the pores of mesoporous silica was observed. The catalysts used in the present study retained their catalytic activity for five reaction cycles. The rate of benzylation of substituted benzenes and benzylating agents was influenced by the electronic nature of the substituent. Electron‐donating groups enhanced the rate of reaction; however, electron‐withdrawing groups retard the benzylation. These results show that the reactivity of benzene and benzyl alcohols was retarded by electron‐withdrawing groups. The formation of polybenzylated products was influenced by the reactivity of diphenylmethane products. The benzylation accompanies the DBE formation by the dehydration of BnOH, particularly in the initial stages, because the benzylation of aromatics with BnOH is not as rapid as the dehydration of BnOH. However, direct benzylation of benzene occurs with DBE and DBE participates in the benzylation of benzene via BnOH after its hydrolysis. This is further supported by the effect of water on the benzylation of benzene by DBE, although there is a possibility of direct benzylation of DBE with benzene. Copyright © 2006 Society of Chemical Industry